1. Field of the Invention
This invention relates to an exhaust monitoring sensor, such as an oxygen sensor, for a closed-loop air-to-fuel ratio control system of a multiplex exhaust manifold engine.
2. Description of the Prior Art
It is known to regulate the air-to-fuel ratio of an air/fuel mixture at an optimal level by means of a closed-loop or feed-back control system in an internal combustion engine. Such a control system typically has an oxygen sensor for sensing oxygen concentration in the exhaust gas, which is indicative of the air-to-fuel ratio. The oxygen sensor is usually attached to an engine exhaust manifold to be exposed to exhaust gas.
Some engines have a dual exhaust manifold which consists of two independent submanifolds. Each of the submanifolds combines the exhaust ducts from a plurality of engine cylinders into a single common passage. The common passages of the two submanifolds are usually adjacent and separated by a common partition wall.
In the case of the above dual-exhaust-manifold engine, the sensing element of the oxygen sensor is disposed in a small hole in the partition wall to be exposed to exhaust gases flowing through both of the exhaust submanifolds. However, such an arrangement of the oxygen sensor entails an extremely small positional tolerance, since the sensing element should be centered within the small hole in the partition wall to ensure the reliability of the sensor.